1. Field of the Invention
The present invention relates to display apparatuses having protective covers, and more particularly to a display apparatus suitable as a liquid-crystal display apparatus.
2. Description of the Background Art
For a display apparatus intended for outdoor use, e.g. a liquid-crystal display apparatus using liquid crystal, it is necessary to protect the display panel from external shock and rainwater. Accordingly, the display surface of the display panel is often covered by a transparent resin or glass protective cover, and the periphery of the protective cover is further waterproofed.
When a protective cover is provided over the display surface of a display panel, an air layer exists between the display panel and the protective cover. Then, the external light entering the display surface reflects at the front and back surfaces of the transparent protective cover and at the surface of the display panel as a flat panel. This degrades visibility.
In some image display apparatuses, in order to solve the deterioration of visibility, the gap between the display panel and the protective cover is filled with transparent resin, or a light-transmitting adhesive sheet (hereinafter referred to also as “a transparent adhesive sheet”) is provided there (for example, see Japanese Patent Application Laid-Open No. 2006-290960).
When the gap between the display panel and the protective cover is filled with transparent resin, the display quality deteriorates as the transparent resin deteriorates with age. For example, when the transparent resin is ultraviolet cured resin, it will be yellowed with age deterioration due to ultraviolet (UV) radiation and the display quality deteriorates.
When a transparent adhesive sheet is provided, age deterioration is not likely to occur, but bubbles are included when the transparent adhesive sheet is bonded. A frame is provided to cover the periphery of the display surface of the display panel, and so there is a step height between the frame and the display surface of the display panel. Accordingly, when a transparent adhesive sheet is provided between the display panel and the protective cover, bubbles will be included in the vicinities of the step height between the frame and the display surface of the display panel, when the transparent adhesive sheet is bonded to the display panel. This considerably degrades display quality.
It is necessary, in order to prevent the inclusion of bubbles, to provide the transparent adhesive sheet only on the display surface of the display panel. However, when the transparent adhesive sheet is provided only on the display surface of the display panel, then the frame, the display panel, and the protective cover cannot be fixed, which lowers shock resistance of the display apparatus.
Japanese Patent Application Laid-Open No. 2009-116297 (hereinafter referred to as patent document) discloses a technique for preventing the inclusion of bubbles without lowering the shock resistance of the display apparatus. In the display apparatus disclosed in this patent document, two transparent adhesive sheets are provided in the gap between the display surface of the display panel and the protective cover. One of the transparent adhesive sheets is provided within the opening of the frame and bonded to the display surface of the display panel. The other transparent adhesive sheet bonds and fixes the transparent adhesive sheet within the opening of the frame, the frame, and the protective cover.
In the display apparatus disclosed in this patent document, one of the two transparent adhesive sheets, the one provided within the opening of the frame, must be positioned such that it does not extend over the opening edges of the frame and such that a gap of a certain or more distance does not remain between the opening edges of the frame and the transparent adhesive sheet. If the transparent adhesive sheet extends over the opening edges of the frame, a step height forms at the opening edges of the frame and bubbles will be included. Also, if there is a certain or more distance between the transparent adhesive sheet and the opening edges of the frame, the edges of the transparent adhesive sheet will be exposed and visually recognized from the opening of the frame, degrading the display quality.
In order to prevent the transparent adhesive sheet within the opening of the frame from extending over the opening edges of the frame, the dimensions of the transparent adhesive sheet must be formed smaller than the opening of the frame such that it will not extend over the opening of edges of the frame. Positioning such a transparent adhesive sheet without a gap between it and the opening edges of the frame requires strict control of the dimensions of the transparent adhesive sheet and the opening of the frame, and the work of positioning the transparent adhesive sheet takes time and effort. Accordingly, the technique disclosed in this patent document has room for improvement.